Centrifugal fans



April 25, 1961 J. D. MURPHY CENTRIFUGAL FANS Filed April 18,

VIIIIIIIIIIIIIIIIIIIIIH Jazzaes D. Mtafjzz y, (412207 2289 2,981,461 "CENTRIFUGAL FANS James D. Murphy, Framingham, Mass., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Apr. 18, 1958, Ser. No. 729,308 2 Claims. (Cl. 230-114) This invention relates to centrifugal fans having rotors without inlet shrouds, and has as objects to improve the eflici'encies of such fans and to vary the.outputs thereof.

Centrifugal fans having rotors with radial blades without inlet shrouds are used for some duties. I have found that a portion of the air or other gas being handled, moving from such blades, flows diagonally from the blades just short of their outer ends, into the lower pressure area nited States Patent a existing between the open sides of the blades and the inlet sheet of the fan.

A feature of my invention is that I increase the widths of the blades of such a rotor at their outer edges so that they have portions extending into the diagonal path of the air which in prior rotors would escape into the lower pressure area, such extended blade portions working on the air which would otherwise escape from the rotor, thereby increasing the pressure provided by the rotor.

I have also found that such an open sided radial bladed rotor induces a vortical flow of air ofif the open outer edges of the blades, which vortical flow rotates in the direction of rotation of the rotor, and does not move downstream to add to the useful output of the fan.

Another feature of my invention is that I make use of such spinning air by using it as a volume control. When a volume reduction is desired, a portion of the spinning air is recirculated as secondary air into the inlet of a rotor, reducing the volume of primary air entering the rotor. The rotor does less work on the spinning air so that volume reduction is accomplished.

My invention will now be described with reference to the annexed drawings, of which:

Fig. 1 is a side elevation, with a portion of the outer inlet sheet removed, of a centrifugal fan embodying my invention;

Fig. 2 is an enlarged section along the line 2-2 of Fig. 1;

Fig. 3 is a side view of the annular damper ring used for varying the volume of air from the fan, and

Fig. 4 is a fragmentary front view of the inner inlet sheet of the fan showing the air inlet slots which are adapted to be covered or uncovered by the damper ring of Fig. 2.

The fan has a conventional scroll-shaped casing 10, and has an inlet sheet 11 with an axial inlet passage 12. The fan has a rotor 13 with radial blades 14 on a hub 15 attached to a rotary shaft 16. The rotor has no inlet shroud so that the front or inlet edges of the blades 14 are unenclosed. The rotor has a back plate 9 which with the hub 15 supports the blades 14. The usual rotor of this type has inlet edges which extend radially from the hub to the outer edges or tips of the blades. The dashed line arrows on Fig. 2 show the path of the air which would escape from the blades of the usual rotor into the lower pressure area between the inlet sheet 11 and the blades.

I add the triangular-shaped blade portions 20 to the blades, which project from the outer ends or tips of the blades towards the inlet sheet and into the escape path of the air from the usual rotor. These blade extensions increase the air pressure by impacting the air tending to flow in such escape path.

The inlet sheet 11 has spaced-apart, annular slots 22 opposite the outer ends of the blades. Slidably supported in a guide 23 attached to the inner surface of the inlet sheet 11 is an annular damper ring 24 having spaced-apart, annular slots 25 corresponding in size and number to'the slots 22 in the inlet sheet 11.

An outer inlet sheet 26, circular in outline, is attached around the edge, around the guide 23, to the inner inlet sheet 11 by bolts 27, and has a central air inlet opening 28 aligned with the inlet passage 12. The outer inlet sheet 26 is spaced from the inner inlet sheet 11 to form a recirculated air passage 30 into which the slots 22 discharge, and which discharges recirculated air into the inlet pas" sage 12.

A damper adjusting rod 31 is attached to the damper ring 24, and extends through a curved slot 32 in the outer inlet sheet 26. A curved baflle 33 slidable in curved guides 34 attached to the outer surface of the sheet 26, is attached to the rod 31, and covers the slot 32 to prevent air leakage from the passage 30 through the slot 22. An adjusting handle 36 on the outer end of the rod 31, has an indicator 37 opposite a scale 38 calibrated in terms of pressure or volume. The handle 36 can be adjusted to move the damper ring 24 to align the slots 25 in the damper ring 24 with the slots 22 in the inlet sheet 11 so that maximum recirculation of the air set spinning by the rotor 11, through the passage 30 into the inlet passage 12 and into the rotor, can take place. At this time maximum volume reduction takes place.

The handle 36 can be adjusted to place the solid parts of the damper ring 24 between the slots 25 across the slots 22 in the inlet sheet 11 so that no recirculation can take place. At this time there is no volume reduction.

The handle 36 can be adjusted to intermediate positions at which the damper slots 25 are partially aligned with the slots 22, for providing partial recirculation and partial volume reduction.

The inlet edges of the blades 14 have slots 48 into which the inner end of the inlet sheet 11 around the passage 12, extends for preventing any recirculation of spinning air into the rotor except through the passage 12.

In operation, the blade extensions 20 impact the air which in the usual unshrouded rotor, escapes from the blades before reaching their outer ends, thereby increasing the air pressure over that which would be provided without such blade extensions.

By adjusting with the handle 36, the damper ring 24 so that its slots 25 are aligned with the slots 22 in the inlet sheet 11, the spinning air from the rotor is supplied, still spinning in the direction of rotor rotation through the recirculation passage 3 3 back into the rotor. T he rotor adds reduced pressure to the spinning air so that the pressure added to the air passing through the rotor is reduced over that which would be added if there was no recirculation.

What I claim is:

1. Acentrifugal fan comprising a rotor having a hub and a backplate, a plurality of radial blades supported by said hub and backplate, said blades having back edges at said backplate and having front edges opposite said back edges which are unenclosed from their roots to their tips, said fan having a casing around said rotor, said casing having an inner inlet sheet with an axial inlet passage, said casing having an outer inlet sheet with an axial inlet opening, said sheets having portions spaced apart around said passage and opening to form a recirculated air passage connecting with said passage in said inner sheet, said inner sheet having spaced-apart recirculated air openings extending therethrough opposite the tips of the said front edges of said blades connecting with the interior of said casing around said rotor and with said recirculated air passage, and means slidable along said inner sheet for opening and closing said recirculated air openings in said inner sheet.

2. A centrifugal fan comprising a rotor having a hub and a back plate, a plurality of spaced-apart, radially extending blades supported at their roots by said hub and supported at their back edges by said backplate, said blades having front edges opposite said back edges which are unenclosed from their roots to their tips, said fan having a casing around said rotor, said casing having an outer inlet sheet with an axial inlet opening, and having an inner sheet with a portion forming an axial inlet passage extending towards said blades, said sheets having portions spaced apart around said passage and said opening to form a recirculated passage connecting with said passage, said inner sheet having spaced-apart, recirculated -a1r openings extending therethrough opposite the tips of said front edges, connecting the interior of said casing with said recirculated air passage.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES German application No. 1,020,761, printed Dec. 12, 1957, KL;27c 13/01. 

